The overall aim of the Program Project is to define the molecular basis of heritable forms of osteoarthritis (OA) and other related diseases affecting articular cartilage. The work proposed is a logical extension of the research completed during the previous period of funding. The primary emphasis of the current application will be to attain a better understanding of the effects of mutations in genes encoding articular cartilage matrix components on the structure and function of the tissue. The secondary aim will be to identify the genetic defects in disorders of articular cartilage that are not caused by mutations in cartilage collagen genes. Project 1 will extend the successful genetic linkage analysis studies that allowed the identification of mutations in the gene encoding the cartilage oligomeric matrix protein (COMP) in patients with multiple epiphyseal dysplasia and pseudo-achondroplasia. The current studies will search for additional mutations in families with these diseases and will employ transgenic mice technology to determine the mechanisms whereby the mutations cause the clinical pheonotypes. Project 2 will focus on the identification of gene locus for familial calcium pyrophosphate deposition disease (CPPDD). Previous studies identified a narrow segment in chromosome 5q containing the mutated gene responsible for the disease. In this project positional cloning and other strategies will be employed to identify the locus for CPPD and the mutation responsible for disease. Project 3 will examine the effects of mutations in the genes for three cartilage-specific collagens (COL2A1, COL9A2, and COMP on the structure and function of cartilage employing long term cultures of human chondrocytes stably transfected with mutated constructs of these genes and will study chondrocytes cultured from transgenic mice harboring various mutations in extracellular matrix genes. Project 4 will extend the successful studies with transgenic mice conducted during the previous funding period in attempts to identify the mechanisms responsible for the alterations in extracellular matrix in mice harboring single mutations in various collagen genes as well as combinations of mutations in genes encoding two distinct collagen genes. We expect that the results of this multifaceted approach will provide a greater understanding on the role that mutations in genes encoding extracellular matrix cartilage proteins play on the pathogenesis of heritable OA and other related cartilage diseases. We also expect that the results will have broader implications towards the understanding of the pathogenetic mechanisms of nonheritable forms of OA.